Two-ply yarn twisting and cabling machines are described in commonly owned U.S. Pat. Nos. 4,163,357 and 4,180,967. These machines allow two separate primary yarns to be wound into a single two-ply yarn. One or both of the yarns, in addition, may itself be twisted. Such an arrangement therefore allows a two-ply yarn to be made with two yarns wound together in, for example, a S-twist, with the yarns themselves being twisted in a Z-twist.
A particular problem with such device is yarn or thread breakage. Unlike a normal single-ply twisting machine with such an apparatus if one of the yarns breaks, the device will still continue to wind up the other yarn. In fact it is possible in such systems for one of the supplies to become depleted or one of the yarns to break and for this problem to go undetected so that a spool or yarn is supplied to a user, with the yarn being single-ply yarn instead of the desired double ply. The results of such an accident can be extremely grave in the production of high-quality textiles.
It has been suggested to provide monitoring equipment for the individual yarns. This is relatively expensive due to the fact that two yarns at least are combiined in each cabling or twisting station of such a machine, which normally includes a plurality of such cabling or twisting stations. It is almost impossible to monitor the condition of yarn being twisted by such a machine, as it normally passes directly from its supply to the center of the twister spindle, and then forms a balloon whence it is fed to the combining location. Nowhere along this path is a convenient place the yarn can be passed through appropriate sensing equipment. No other solutions of this problem have met with any success.